The present invention relates generally to a giant magnetoresistive sensor for use in a magnetic read head. In particular, the present invention relates to a giant magnetoresistive read sensor having an enhanced giant magnetoresistive response.
Giant magnetoresistive (GMR) read sensors are used in magnetic data storage systems to detect magnetically-encoded information stored on a magnetic data storage medium such as a magnetic disc. A time-dependent magnetic field from a magnetic medium directly modulates the resistivity of the GMR read sensor. A change in resistance of the GMR read sensor can be detected by passing a sense current through the GMR read sensor and measuring the voltage across the GMR read sensor. The resulting signal can be used to recover the encoded information from the magnetic medium.
A typical GMR read sensor configuration is the GMR spin valve, in which the GMR read sensor is a multi-layered structure formed of a nonmagnetic spacer layer positioned between a synthetic antiferromagnet and a ferromagnetic free layer. The magnetization of the synthetic antiferromagnet is fixed, typically normal to an air bearing surface of the GMR read sensor, while the magnetization of the free layer rotates freely in response to an external magnetic field. The synthetic antiferromagnet includes a reference layer and a pinned layer which are magnetically coupled by a coupling layer such that the magnetization direction of the reference layer is opposite to the magnetization of the pinned layer. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the reference layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect, i.e. greater sensitivity and higher total change in resistance, than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer.
A pinning layer is typically exchange coupled to the pinned layer of the synthetic antiferromagnet to fix the magnetization of the pinned layer in a predetermined direction. The pinning layer is typically formed of an antiferromagnetic material. In antiferromagnetic materials, the magnetic moments of adjacent atoms point in opposite directions and, thus, there is no net magnetic moment in the material.
An underlayer is typically used to promote the texture of the pinning layer consequently grown on top of it. The underlayer is typically formed of a ferromagnetic material and is chosen such that its atomic structure, or arrangement, corresponds with a desired crystallographic direction.
A seed layer is typically used to enhance the grain growth of the layers consequently grown on top of it. In particular, the seed layer provides a desired grain structure and size for the underlayer.
One principal concern in the performance of GMR read sensors is the xcex94R (the maximum absolute change in resistance of the GMR read sensor), which directly affects the GMR ratio. The GMR ratio (the maximum absolute change in resistance of the GMR read sensor divided by the resistance of the GMR read sensor multiplied by 100%) determines the magnetoresistive effect of the GMR read sensor. Ultimately, a higher GMR ratio yields a GMR read sensor with a greater magnetoresistive effect which is capable of detecting information from a magnetic medium with a higher linear density of data.
A key determinant of the GMR ratio is the amount of parasitic shunting current flowing through the GMR read sensor. The GMR signal produced by the GMR read sensor is generated by the current flowing through the free layer, the spacer layer, and the reference layer of the synthetic antiferromagnet. Current flowing through any other layer is a parasitic shunting current, and reduces the GMR signal. As a result, the less parasitic shunting current that is present in the GMR read sensor, the greater the GMR ratio. Parasitic shunting current can be reduced by increasing the resistivity of the layers that do not contribute directly to the GMR signal. In particular, increasing the resistivities of the pinning layer and the underlayer is especially desirable because these layers are typically formed of magnetic materials with low resistivities. In these instances, however, it is important to ensure that the magnetic properties of these layers are maintained in order for the GMR read sensor to function properly.
The present invention addresses these and other needs, and offers other advantages over current devices.
The present invention is a giant magnetoresistive stack for use in a magnetic read head. The giant magnetoresistive stack has a plurality of layers including at least one ferromagnetic layer which contributes to a giant magnetoresistive signal, and at least one doped ferromagnetic layer which does not contribute to a giant magnetoresistive signal. The dopant in the doped ferromagnetic layer reduces parasitic shunting current through the giant magnetoresistive stack by providing an increase in resistivity without a decrease in magnetization.